Effect of heat on Group 2 carbonates

You should have seen from the video that the stability of the carbonates towards heat increased as we went down the group. This is linked to the size of the ion which is illustrated in the table below:

Cation	Ionic radius (nm)	Time to cloudiness (s)	Degree of cloudiness	Decomposition Temperature (K)
Mg²⁺	0.072	27	high	813
Ca²⁺	0.100	80	medium	1173
Sr²⁺	0.113	120	slight	1563
Ba²⁺	0.136	-	very slight	1573

The explanation behind this is that the smaller group 2 cations have a greater polarizing effect on the carbonate ion, causing it to decompose to a metal oxide and carbon dioxide gas more readily. The equations are all very similar:

MgCO₃(s) ⇒ MgO(s) + CO₂(g)	CaCO₃(s) ⇒ CaO(s) + CO₂(g)
SrCO₃(s) ⇒ SrO(s) + CO₂(g)	BaCO₃(s) ⇒ BaO(s) + CO₂(g)

The polarising effect is much less with a 1+ ion. Most group1 carbonates do not decompose under normal heating. Only lithium carbonate (with the smallest positive ion) decomposes in the same way as the group 2 carbonates.